1. Field of the Invention
This invention relates to injectors, such as are used by insulin users.
2. Description of the Related Art
The trend has been to provide those patients who are required to regularly self-inject with automatic injection devices which can provide multiple doses. It is obviously desirable to ensure that the correct dosage volume is delivered each time but the correct dosage volume will vary from patient to patient. It is therefore equally desirable to provide a system which can deliver dose units so that a user can deliver the right number of units for their condition. There are therefore attractions in providing an electronically controlled system but any such system must be fail safe.
Typically injectors are mechanical and work on the basis of a pen like injector into which a disposable drug cartridge can be introduced. The cartridge is arranged to receive a hypodermic needle. With current systems it can be difficult to monitor dose units where a cartridge is not sufficiently full to deliver the whole required dose.